Flow control features for fluid filtration device and methods

ABSTRACT

A fluid filtration device is provided that can be used for separating solids from fluids. In some embodiments, the fluid filtration device comprises a hollow housing and a hollow filter assembly located within the housing. Fluid to be filtered is provided to the inside of a filter material in the filter assembly and passes outward toward the housing. In some embodiments one or more flow-directing features are located between the filter assembly and the housing, and may aid in the flow of fluid to a filtered outlet after passing through the filter. The flow-directing features may comprise, for example, channels that extend the length of the filter.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

1. Field of the Invention

The present application relates to the filtration of particles fromfluid streams, and more specifically to filter systems and their use.

2. Description of the Related Art

Filter systems contain cleaning devices, such as cleaning brushes,suction scanning devices, and back flush mechanisms. These devices aredriven by various means including by hand, motor, turbine or vortex.However, existing fluid filtration devices have difficulty handlinglarge concentrations of solids in the fluid stream. Generally cleaningmechanisms which can operate continuously while the system is filteringout-perform those which require the filtration system to be stopped forcleaning. And still, existing continuous cleaning mechanisms oftensuffer from premature fouling when the particle accumulation rateexceeds their limited cleaning rates.

SUMMARY OF THE INVENTION

In some aspects a fluid filtration device is provided. The fluidfiltration device may be used, for example, to separate solids fromfluids. In some embodiments a fluid filtration device comprises a hollowhousing comprising an inlet and a filtered outlet. A hollow filterassembly may be located inside the housing. The filter assembly maycomprise a filter material having an interior surface and an exteriorsurface. In some embodiments the housing and filter assembly may becylindrical. A cleaning assembly may be located within the housing insome embodiments. In some embodiments a cleaning assembly is locatedinside the filter. In some embodiments the cleaning assembly is arotating cleaning assembly. The cleaning assembly may comprise adistributor for providing fluid to the interior surface of the filter.In some embodiments the cleaning assembly comprises a rotatingdistributor and one or more wipers. In some embodiments a cleaningassembly is not provided inside the filter.

The device may comprise one or more flow-directing elements to directfluid that has passed through the filter toward the filtered outlet. Insome embodiments a device comprising flow-directing elements does notcomprise a cleaning assembly, such as a cleaning assembly located withinthe filter. In some embodiments the flow-directing features may be usedin combination with disposable bag or cartridge filters, or withself-cleaning filters like backflushing filters.

In some embodiments one or more flow-directing channels may be locatedbetween the filter assembly and the inside of the housing. Theflow-directing channels may be arranged such that they direct fluidtoward the filtered outlet after it passes through the filter material.In some embodiments the channels run the entire length of the filterand/or filter assembly. In some embodiments the channels extend aportion of the length of the filter and/or filter assembly. In someembodiments the channels begin below the top of the filter and/or filterassembly. In some embodiments a region above the channel allows eachchannel to communicate with an air release outlet. An unfiltered regionmay additionally communicate with an air release outlet.

The channels may have a consistent cross section throughout theirlength. In some embodiments the cross section of the channels may varyat one or more places along their length. In some embodiments thechannels get wider in the direction of flow. The shape of the channelsmay be selected such that the fluid flows at an approximately constantrate the length of the channels. In addition, in some embodiments one ormore bumps, divets, ridges or the like may be present in the channels.These features may serve to create turbulence in the fluid flow.

In some embodiments the channels are formed from one or more baffles.The baffels may be oriented with the axis of the filters and thus definethe one or more channels. In some embodiments the baffles run the entirelength of the filter and/or filter assembly. In some embodiments thebaffles extend a portion of the length of the filter and/or filterassembly. In some embodiments the baffles begin below the top of thefilter and/or filter assembly. The baffles may define channels thatcomprise a consistent cross section throughout their length. In someembodiments the baffles define channels that have a variable crosssection along their length. For example, the baffles may be such thatthe channels get wider in the direction of flow, such as in thedirection of the filtered outlet.

The baffles may be attached to the filter assembly, the housing, orboth. In some embodiments the one or more baffles are attached to thehousing. The baffles may serve to align the filter in the housing.

In some embodiments the channels are at least partially formed from thehousing itself. In some embodiments the channels are at least partiallyformed from the filter assembly.

In another aspect methods of filtering a fluid are provided. The methodsmay comprise providing a filtration device as described herein andpassing a fluid through the device. In some embodiment a filtrationdevice is provided comprising a housing, an annular filter locatedwithin the housing and one or more channels defined between the filterand the housing. The channels may be oriented with the axis of thefilter and extend along the length of the filter. Fluid is fed to theinside of the filter, such as through a distributor. Fluid passesthrough the filter and the one or more channels direct the fluid towardan outlet region after passing through the filter.

In some embodiments, the one or more channels are defined by one or morebaffles. The channels may also be formed, at least in part, by thehousing itself and/or by a filter assembly that holds the filter. Insome embodiments baffles may be attached to the housing and extendtoward the filter. In addition to directing fluid flow, the baffles mayalso serve in some embodiments to align the filter within the housing.

In some embodiments the channels have a consistent cross sectionthroughout their length. In some embodiments the channels have a crosssection that expands along at least a portion of the length of thechannel. For example the channel may expand as it approaches a filteredoutlet. The channels may also comprise one or more bumps ridges ordivets, which serve to create turbulence in the flow of fluid throughthe channels.

In some embodiments the channels are configured such that the flow rateof fluid through the channels is relatively constant.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached figures various embodiments are illustrated by way ofexample. Like reference numerals refer to similar elements.

FIG. 1 is an exploded view illustrating each of the major components ofone embodiment of a filter system.

FIG. 2 is an illustration of one embodiment of the filter system wherethe filter is sealed to the housing at either end, and the cleaningassembly comprises wipers. The housing, filter and lid are shown incutaway form while the cleaning assembly is not.

FIG. 3 is an illustration of another embodiment of the filter systemwhere the filter assembly is sealed to the housing at either end, andthe cleaning assembly comprises wipers and a distributor. The housing,filter and lid are shown in cutaway form while the cleaning assembly isnot.

FIG. 4 is an illustration of an embodiment of the filter system wherethe filter assembly is sealed to the housing at one end and the lid atthe other end, and the cleaning assembly comprises wipers and adistributor. The housing, filter and lid are shown in cutaway form whilethe cleaning assembly is not.

FIG. 5 illustrates an embodiment of the filter assembly comprising afilter support structure and a filter material.

FIG. 6 is a schematic illustration of a cross-section of a filtermaterial having a smooth working surface and expanding pores.

FIG. 7 is a schematic illustration of a cross-section of a filtermaterial having expanding pores and a smooth working surface wherein theboundary of the pore opening at the minimum width of the pore opening(the narrowest part of the pore) substantially defines the highest localpoint on the working surface.

FIG. 8 illustrates a portion of the surface of a filter materialcomprising an alternating pattern of slotted pores.

FIG. 9 illustrates a portion of the surface of a filter materialcomprising a non-alternating pattern of slotted pores.

FIG. 10 illustrates a groove on a cleaning assembly which captures theflexible backing of a wiper.

FIG. 11 illustrates an embodiment of the cleaning assembly comprising adistributor with evenly spaced holes arranged in a spiral pattern.

FIG. 12 illustrates an embodiment of the cleaning assembly comprising adistributor with slots arranged in a spiral pattern.

FIG. 13 illustrates an embodiment of the filter system in cutawayshowing the cleaning assembly supported by the inlet tube.

FIG. 14 illustrates an embodiment of the filter system in cutawayshowing the cleaning assembly supported by a drive shaft at one end ofthe housing.

FIG. 15 is an embodiment of the cleaning assembly where the spiral wiperforms a divider which divides the collection region from thedistribution region of the housing.

FIG. 16 is a schematic representation of a filter system with anarrangement of various fluid system components that may be used tooperate the filter system.

FIG. 17 illustrates an embodiment comprising an inlet housing, an outlethousing and a lid.

FIG. 18 illustrates an embodiment of the cleaning assembly.

FIG. 19 illustrates an embodiment of the filter assembly.

FIG. 20 illustrates an embodiment of a filtration device in cutawayview.

FIG. 21 illustrates a housing in exploded view.

FIG. 22 shows insertion of a cleaning assembly into a housing.

FIG. 23 shows a filter being inserted into a housing.

FIG. 24 illustrates an embodiment of a housing comprising baffles.

FIG. 25 shows a cutaway view of a housing filter and cleaning assembly.

DETAILED DESCRIPTION

The methods, systems and components described herein relate to filtersystems for separating solids from fluids. The fluids may comprise airor other gas; or water, oil, fuel or other liquid. In some applicationsthe filtered fluid is the end product. Such applications may include,but are not limited to, drinking water, wastewater, recycled water,irrigation, swimming pools, food and beverage processing, produced waterfrom oil and gas production, cooling towers, power plants, and marineballast or bilge water. By way of example, drinking water is oftenproduced by a series of filters removing ever finer particles andcontaminants. A first or second level of filtration may comprise anautomatic strainer to remove particles down to 10 microns in diameter.The filtered water would then be conveyed to a finer filter like anultrafilter, microfilter or reverse osmosis filter. Some embodiments ofthe filter systems described herein are well suited to this application.

In other applications, such as biofuel production and other biomasstechnologies, a particulate is separated from a fluid stream and thefiltered solid is the desired product. By way of example, algae may beharvested from the water in which it's growing for the purposes ofmaking biodiesel. The algae is first filtered from the water andconcentrated to form a slurry. The oil is extracted from the algae bysolvent extraction or other means, and then converted into biodieselthrough a chemical process called transesterification. Some embodimentsof the filter systems described herein are well suited to remove algaefrom its liquid growth media for these purposes.

Housing and Lid Assembly

In some embodiments, a filter system comprises a hollow housing and ahollow filter assembly. The filter system may also comprise a cleaningassembly and a lid assembly. One embodiment of such a filter system isillustrated in FIG. 1. The filter system 10 as illustrated in FIG. 1comprises a hollow housing 100, a hollow filter assembly 200, a cleaningassembly 300, and a lid assembly 400.

The hollow housing may take any of a variety of shapes. In theillustrated embodiment the hollow housing 100 is generally cylindricalin shape and may comprise one or more parts coupled together, such as byfasteners, a v-band clamp or other suitable connectors. Additionally theillustrated filter system 10 has a lid assembly 400 at one end of thehousing 100 which can also couple to the housing 100, for example by oneor more fasteners, a v-band clamp, or other suitable connectors. Thehousing 100 and lid assembly 400 may be fabricated from one or more of avariety of materials, examples of which are plastic, fiber glass,stainless steel, and epoxy coated steel.

The filter assembly is shaped to fit within the hollow housing and insome embodiments is annular in shape. As illustrated, the filterassembly 200 takes the shape of a hollow cylinder and is located insideand concentric with the housing 100. The filter assembly 200 comprises afilter material, such as a filter membrane, and in some embodiments maycomprise a filter frame or other support structure. In some embodimentsthe filter assembly is generally open at both ends and contacts thehousing, for example through a seal at one or both ends. Examples ofseals are o-rings, x-rings, u-cups and gaskets. In the illustratedembodiment, the filter assembly 200 seals to the housing 100 at one endand the lid assembly 400 at the other end. The lid as well as the otherend of the housing can be flat, semi-elliptical, hemispherical, or othersuitable shape.

The housing and lid combination have one or more each of an inlet, afiltered outlet and a drain outlet. In some embodiments one or moreinlets are generally located at one end of the filter system, while oneor more filtered outlets and drain outlets are generally located atopposite ends of the filter system from the one or more inlets. In otherembodiments, other arrangements may be used. The one or more inlets andoutlets may be positioned on any combination of the side wall of thehousing, the end of the housing, and the lid. Inlets provide a path forfluid to flow from a source to the interior of the filter assembly whereit contacts the working surface of the filter material. The filteredoutlet provides a path for fluid that has passed through the filtermaterial to exit the housing. Drain outlets provide a path for fluidand/or solids that do not pass through the filter material to be removedfrom the housing.

When the filter assembly is sealed to the housing, as illustrated inFIGS. 2 and 3, or the housing and lid as illustrated in FIG. 4, anunfiltered influent region 210 and a filtered effluent region 212 arecreated which communicate only through the filter material 214. Theinlet 101, inlet region 118 and drain outlet 103 communicate with theinfluent region 210 at the inside of the filter 214, while the filteredoutlet 102 communicates with the filtered effluent region 212 at theoutside of the filter 214. The drain outlet 103 may be in communicationwith a collection region 116 where unfiltered fluid and filtered solidscollect. Solids that collect on the working surface of the filtermaterial 214 during operation of the filter system 10 may be moved bythe action of wipers 316 to the collection region. A divider 325 may belocated between the collection region 116 and the unfiltered region 210.In some embodiments, for example when the filtered fluid is a liquid,the filtered outlet 102 is located and the housing oriented tofacilitate the expulsion of air from the system. This can beaccomplished, for example, by positioning the filtered outlet 102 at orabove the highest point of the filter material 214. In this way there islittle to no need for an air purge valve. However, such an orientationof the filtered outlet 102 and housing are not required and in someembodiments the housing 100 comprises an air purge valve.

FIGS. 2 and 3 illustrate embodiments where the inlet 101 is located atthe same end of the housing as the filtered outlet 102, albeit onopposite side walls. FIG. 4 illustrates another embodiment where theinlet 101 is located at the same end of the housing as the drain outlet103.

Filter Assembly

In some embodiments a hollow cylindrical filter assembly 200 comprises afilter material 232 and a support structure 230, as illustrated in FIG.5. In some embodiments, however, the filter material 232 will notrequire a support structure 230 and thus a support structure will not beused. In some embodiments the filter material is a surface filter. Inthe embodiments illustrated in FIGS. 2, 3 and 4, fluid passes from theinfluent region 210 at the inside of the filter to the effluent region212 at the outside of the filter. In this way filtered particles collecton the inner, working surface of the filter 214. Suitable filtermaterials include but are not limited to electroformed screens, stackeddisc filters, fabrics and membranes, woven metals, etched metal screens,and wedge wire filters. The filter material may be arranged to form anannular structure, as in the embodiment illustrated in FIG. 5.

In some embodiments a support structure is used. For example, with thinfilter materials, such as screens, fabrics and other membranes, asupport structure may be used to maintain the desired shape, typicallyan annular or cylindrical shape. The support structure may also containseals at each end of the filter or make contact with seals at each endof the housing. In some embodiments a PVC plastic support structure isused to support a hollow cylindrical filter material. In otherembodiments, a support structure comprises openings, where the openingsare covered with the filter material.

A support structure may consist of one or more parts. As illustrated inFIG. 5, the support structure 230 may be assembled from three pieceswhich include two solid tubular end caps 201 and a supportive midsection 202 with a mesh of ribs 238. The end caps 201 may each comprisea seal. For example, each end cap 201 may have an o-ring groove tocontain an o-ring seal 220. In embodiments where the support 230 is madeof PVC, PVC solvent cement may be used to join the three structuralpieces and simultaneously capture the open ends of the filter materialcylinder. In other embodiments of the filter assembly the filtermaterial is placed in an injection mold and the frame is molded directlyonto the filter material in one or more stages. A plastic frame can bemade from any number of suitable plastics including, for example, PVC,polypropylene and polycarbonate. In other embodiments of the inventionthe one or more support structure parts are made from stainless steel orother suitable materials and welded or bonded to the filter material. Infurther embodiments the supportive midsection is made from an overwrapof a screen material which can be, for example, plastic or metal and canbe welded or bonded to the filter material. In other embodiments thefilter material may be supported by a wedge wire wrapped in a spiralshape around the outside of the filter material.

The difference in pressure across the filter material, also referred toherein as transmembrane pressure (even though the filter material is notalways a membrane), causes flow through the filter material. Thetransmembrane pressure is typically maintained at a constant valuethroughout the filtering process, but may be varied in certaincircumstances, such as for cleaning. In some embodiments thetransmembrane pressure may be about 10 psi or less, for example about0.1 to 10 psi. In other embodiments the transmembrane pressure may beabout 0.1 to 3 psi, 0.1 to 2 psi, or 0.1 to 1 psi. A sudden jump in thepressure can occur if the filter suddenly plugs. For this reason thefilter is generally designed to sustain differential pressures in therange of at least 20 to 30 psi, but in some embodiments may sustainpressures as high as 150 psi or more.

As mentioned above, suitable filter materials include but are notlimited to electroformed screens, stacked disc filters, fabrics andmembranes, such as plastic fabrics and membranes, woven metals, etchedmetal screens, and wedge wire filters. In some embodiments, the filtermaterial comprises pores with a maximum width of about 0.1 micron toabout 1500 microns. In other embodiments, the pores may have a maximumwidth of about 1 to about 500 microns or about 1 to about 50 microns.The variation in pore width across a filter can be an important featureof the filter material. In some embodiments the absolute variation inpore width is minimized. It is also common to measure the variation as apercentage of pore width. In some embodiments the variation in porewidth may range from about ±1% to about ±30%. In other embodiments suchas with precision electroformed screens the precision may be measured inmicrons ranging from about ±0.1 micron to about ±5 microns. In someembodiments the filter material comprises expanding pores, which arenarrower at the working surface than at the opposite surface. However, avariety of pore shapes may be used and a filter material having poreswith an appropriate width, shape and other attributes can be selected bythe skilled artisan for a particular application.

In some embodiments the filter material is a precision electroformedscreen. The electroformed screen can be made from a number of materialsfor example nickel, gold, platinum and copper. A filter material of thistype may comprise a substantially smooth working surface and regularlyshaped expanding pores. That is, the pores are narrower at the workingsurface than at the opposite surface. In some embodiments the pores maybe conical. Screens of this type may be used that have pores ranging insize from about 1500 microns down to about 0.1 micron at the narrowestpoint, but variations of the technology can utilize larger or smallerpores. In some embodiments a precision electroformed screen is used forfiltration in the range of 5 to 50 microns and has pores with acorresponding width at the narrowest point.

In some embodiments a filter material is used that comprises a precisionelectroformed nickel screen. One such screen is called Veconic PlusSmooth, fabricated by and available from Stork Veco BV of TheNetherlands. Veconic Plus Smooth is especially well suited to filtrationin the range of about 5 to 50 microns.

A filter material may comprise pores where the internal surfaces of apore may be straight, concave or convex. In some embodiments, asillustrated in FIG. 6, the filter material 232 comprises pores where theprofile of the pore is substantially narrowest at the working surface214 of the filter. In some embodiments where the filter is a cylindricalor annular filter, the working surface may be the internal surface. Thepore may remain the same width or become wider across the filter fromthe internal or interior working surface to the external or exteriorsurface. In some embodiments the pores comprise an expanding region 236and open progressively wider from the working surface towards theopposite surface. In this way, particles 242 small enough to enter apore opening 234 have little or no chance of getting stuck inside a pore236. Surface filters of this type trap particles 240 that are too largeto pass through the filter material on their working surface 214, oftenat the mouth of a pore 234, where they can be acted upon by a cleaningmechanism.

In some embodiments the working surface of the filter is smooth. Thoughthe smooth working surface of the filter may be substantially flat, itmay also have small, uneven features, for example as illustrated in FIG.7. These uneven features may be sudden steps 238 or gradual valleys 239.However, the filter is preferably structured such that during filtrationparticles that are not able to pass through the pores are retained atthe highest local point on the working surface.

In some embodiments the narrowest part of the pore opening 233substantially defines the highest point on the working surface 214 inthe vicinity of the pore. In other embodiments, the narrowest part ofthe pore opening 231 may be slightly below the highest local point onthe smooth working surface 214, for example the narrowest part of thepore opening may be at a depth less than half the width of the poreopening. Thus, for a pore with a narrowest opening of 20 microns, the 20micron opening would be less than 10 microns below the highest point onthe smooth working surface in the vicinity of the pore. This makes itpossible for a cleaning mechanism to make substantial contact with poreblocking particles 240 and wipe them away from the pore openings. Thearea of filter material between the pores is referred to as the bars252.

The pores can have many planform shapes, examples of which are circular,square or slotted. Slotted pores 250 which are longer than they arewide, as illustrated in FIGS. 8 and 9, are used in some embodiments andtend to offer less fluid resistance than a number of smaller circular orsquare pores having the same combined open area. The drawback of slottedpores 250 is that they can pass long skinny particles that areessentially larger than the slot width, but these particles are muchless common. Nevertheless, in some embodiments circular, square orirregularly shaped pores are used.

In some embodiments, filters may have a thickness of about 10 to 10,000microns. This is illustrated as the bar thickness 253 in an exemplaryembodiment in FIG. 7. Electroformed nickel screens, as used in someembodiments, generally have a thickness of 150 to 300 microns, thoughthey may be thicker or thinner. A sheet of filter material has manypores, and in some embodiments substantially all of the pores haveapproximately the same length and width. The pores may be any shape. Insome embodiments they are circular. In other embodiments the pores arelonger than they are wide. In some embodiments the length of each poreis generally about 400 to 500 microns, for example about 430 microns,but may be larger or smaller. The width of the pores may be selected forthe particular filtration application. In some embodiments, widths inthe range of about 0.1 to about 1500, 1 to 500 or 1 to 50 microns areused. In some applications, like the harvesting of microalgae or yeastcells without flocculation, widths from about 0.1 to about 1 micron maybe used.

In some embodiments the pores may be generally arranged in analternating checkerboard pattern as with the pores 252 in FIG. 8, butmay also be arranged in a non-alternating pattern, as in FIG. 9. Thebars 253 are also shown in FIGS. 8 and 9. Screens with non-alternatingpatterns are generally more brittle than those with alternatingpatterns, which tend to be more flexible.

In some embodiments the cumulative open area of all the pores for afilter material is maximized in order to maximize the filtrate rate. Forsmaller pores the number of pores per unit length can be maximized inany given direction. With many screens, such as electroformed nickelscreens that have expanding pores, the maximum open area of pores tendsto be inversely proportional to the sheet thickness, i.e. thicker sheetshave fewer pores. The number of pores per unit length in a givendirection is influenced by many variables, one of which is thelithographic process by which the screens are made.

In some embodiments a screen may have a thickness of about 200 micronswith pores which are about 20 microns wide by about 430 microns long andarranged in a mesh of about 160 pores per inch (6299 m⁻¹) in thedirection perpendicular to the slots and about 40 pores per inch (1575m⁻¹) parallel to the slots. This equates to an open area of about 9%.

In some embodiments the filter material takes the form of a hollowstructure such as a hollow cylindrical or annular structure. Seamlesshollow cylinders can be used and can be fabricated, for example, in anelectroforming process. In other embodiments, cylinders can be made fromsheets of filter material which are then seam welded into a cylinder.Methods of joining seam edges are known in the art and may include, forexample, resistance welding or soldering. In this way cylinders offilter material of any size and length can be made.

In some embodiments a filter material, such as an electroformed nickelscreen or other type of electroformed metal screen, is initially made ina square sheet, such as a sheet one meter on each side, and then trimmedto the proper size for the filter. Filter material may be made in largeror smaller sheets depending on the way they are manufactured, forexample depending on the available electroforming equipment. The trimmedsheet is flexible and is held in the shape of a cylinder while the seamedges are resistance welded, silver solder or joined by another processknown to someone skilled in the art.

In some embodiments, the filter material is coated with one or morematerials to provide or improve a desired property. For example,coatings of nickel-phosphorus alloy, chrome alloy or other suitablemetal alloys may be used to impart attributes such as hardness andcorrosion resistance. In other examples, a filter material may be coatedwith silver for its antimicrobial properties or a composite containingPTFE for its low friction. In some embodiments, an electroformed nickelscreen generally comprises a nickel base and may include one or moreadditional coatings, such as those described above.

Filter fouling generally occurs in two stages. Initially particles blockthe pores of the filter material reducing the effective open area. Thisis simply called “pore blocking.” Secondly a layer of particles collectsat the filter material surface creating what is called a “cake” layerand this causes an ever decreasing filtrate rate. Crossflow filtrationhas been shown to be effective in delaying fouling, for example inconjunction with electroformed nickel screens. This mode of operation isgenerally considered the elegant solution to filter fouling, but thecrossflow stream limits the ultimate recovery rate of influent wherefiltrate is the desired product; and consequently limits the maximumsolids concentration in applications, such as algae and yeastharvesting, where rejectate is the product.

Surface filters are well suited to be cleaned in place throughmechanical means. A number of automated mechanical cleaning technologiesmay be used, alone or in combination, in various embodiments of thedisclosed filter systems and methods. In some embodiments backflushingmay be used. In backflushing the forward flow through the filter isentirely stopped and temporarily reversed to dislodge the pore blockingparticles as well as the entire cake layer. This backflush liquidcontaining solids is discarded through an exhaust valve, such as a drainoutlet. It is sometimes combined with the operation of a cleaning brushor wiper to aid the cleaning of the filter screen. In other embodimentssuction scanning may be used. Here one or more nozzles scan the filtersurface. These nozzles have a large suction force causing liquid to flowbackward locally through the filter screen in the vicinity of thenozzle. This pulls the filter cake off the screen and sends it to anexhaust valve where it is discarded. In this way a small portion of thefilter screen is being cleaned while the rest of the screen continues tooperate normally. While general backflush filters have downtime duringtheir cleaning cycle, suction scanning filters continue to operatealbeit at a lower net flux rate. As with crossflow filtration, thebackflush stream in both systems limits the ultimate recovery rate ofinfluent where filtrate is the desired product; and limits the maximumsolids concentration where rejectate is the product.

In some embodiments of the invention described herein, the filtermaterial is cleaned exclusively by use of a wiper. Thus, backflushand/or crossflow are not employed. In other embodiments, the filtermaterial is cleaned by backflush or crossflow. In some embodiments thefilter material is cleaned by a wiper in conjunction with a backflush,crossflow or both. Electroformed nickel screens which have expandingpores and a smooth working surface are well suited to be cleaned by awiper.

During cleaning the rejected particles move across the surface of thefilter material, for example by means of a wiper and/or a crossflowvelocity. It is generally advantageous to orient the slotted pores ofthe filter material with their long dimension substantiallyperpendicular to the likely path of a rejected particle. Thus in someembodiments the filter material comprises slotted pores that areoriented such that the long aspect of the pores is perpendicular to thedirection of movement of a wiper.

When a wiper is substantially straight and rotates inside a cylindricalfilter, particles move more circularly around the filter than axiallydown the filter. In this case the slots may be oriented with the axis offilter.

A wiper may also take the form of a spiral in which case the particlesmay be pushed along a spiral path on the surface of a cylindricalfilter. Depending on the pitch of the spiral, the path may be more alongthe axis of the filter or more along the circumference of the filter. Ifthe filter material comprises slotted pores, the slots can be orientedperpendicular to that path, though a pure axial or circumferentialorientation is used in some embodiments, for example due tomanufacturing limitations.

Cleaning Assembly—Wipers

A cleaning assembly may be positioned inside the filter assembly and insome embodiments comprises one or more wipers, for example asillustrated in FIG. 2. Fluid may move from the inlet of the housing tocontact the inside wall of the filter material by passing around thecleaning assembly, for example as illustrated in FIG. 2, or through thecleaning assembly, for example as illustrated in FIGS. 3 and 4. Filteredparticles collect on the inner working surface of the filter and whenthe cleaning assembly is rotated the wipers clean the working surface ofthe filter generally by moving filtered particles along the surface andcollecting them ahead of the wiper. The wipers may also lift particlesoff the surface back into the fluid or on to the wipers themselves.

The one or more wipers may be straight or take other useful shapes. Insome embodiments the wipers take a substantially spiral shape along thelength of the cleaning assembly. See, for example, wipers 316 in FIGS. 3and 4. In some embodiments the cleaning assembly comprises a singlespiral-shaped wiper. In other embodiments, the cleaning assemblycomprises two or more spiral shaped wipers. Spiral shaped wipers pushparticles along the filter surface towards one end of the housing, wherethey can be collected in a collection region. The concentration ofparticles on the wiper will typically increase in the direction of thecollection region of the housing.

In some embodiments one or more spiral shaped wipers have a fixed pitchand in other embodiments they have a variable pitch. A typical pitch ofthe spiral wiper, for example for a cylindrical filter that is 4 inchesin diameter, would be one complete turn for every 6 inches of cleaningassembly or, in other words, 60 degrees per inch, but could be less ormore. In some embodiments the spiral wiper or wipers have a pitch ofabout 10 to about 360 degrees per inch. Variable pitched wipers have apitch that changes along the length of the cleaning assembly toaccommodate the buildup of particles on the wiper. By way of example,the pitch may change from 10 degrees per inch at the far end of thecleaning assembly to 360 degrees per inch at the end closest to thecollection region.

It is generally advantageous to limit the speed of the wipers along thesurface of the filter to less than 100 inches per second but this valuemay be higher or lower depending on the filter and wiper design. Inembodiments in which the wiper touches the filter material, frictionbetween the wipers and the filter material causes wear of the wipers,filter material or both. Faster wipers tend to create more turbulence inthe unfiltered region of the housing which may interfere with themovement of particles towards the collection region. The wipers may alsobreak particles apart into smaller particles which then pass through thefilter material. When the wiper speed is limited, the cleaning frequencyon the material can be increased by adding more wipers. A cleaningassembly will typically have from about 1 to about 10 wipers, forexample 2, 4, or 8 wipers, but may have more or less.

Wipers may take many forms examples of which are brushes, squeegees andscrapers and may be rigid or flexible. In one embodiment multiple wipersall take the same form and in other embodiments multiple wipers take acombination of forms. Brushes are generally made from non-abrasiveplastic fibers like nylon, polypropylene, or polyester, though they maybe made from other suitable materials. As particles decrease in size,brushes tend to be less effective and squeegees become more effective.Squeegees may be made from any number of common natural or syntheticrubbers, an example of which is polyurethane. In other embodiments oneor more wipers may comprise a scraper. The scraper may be made from anynumber of suitable plastics such as polycarbonate and PTFE, or othersuitable materials.

In some embodiments one or more of the wipers are preloaded against thesurface of the filter by deflecting the wiper, such as a brush orsqueegee. In other embodiments at least one of the wipers 316 does nottouch the surface 214 of the filter but extends to a height slightlyabove the surface. In some embodiments the wipers may extend to betweenabout 0.001 to 0.1 inches from the surface of the filter, 0.01 inchesfor example. In this way, circulation of the wipers may create a localcrossflow of fluid which tends to push particles along the surface,while the wipers do not actually touch the surface of the filtermaterial.

The wipers may be supported by a structure at one or both ends and/or bya center structure as in FIGS. 2, 3 and 4. The center structure may besolid or hollow and take any number of suitable cross sectional shapes,examples of which are round and polygonal. In one embodiment of theinvention the center structure is substantially round and has one ormore grooves on its exterior surface. As illustrated in FIG. 10, a wiper316 may have a flexible backing 322 which is inserted into the groove320 on the center structure. In some embodiments a wiper is glued into agroove 320. In other embodiment the groove 320, as in FIG. 10, has adovetail or other suitable shape to retain a wiper 316. In oneembodiment a wiper is held in place by friction along the length of thegroove. In other embodiments a wiper is retained at each end by a plug,end cap, or other suitable means. In other embodiments one or morewipers are glued to a smooth support structure. As mentioned above, inother embodiments the wipers are self-supporting and are not attached toa support structure that runs the length of the wipers. However, theymay be supported at one or both ends.

Cleaning Assembly—Distributor

In some embodiments the center structure of the cleaning assemblycomprises a hollow tube which can act as a distributor for the filterassembly. The hollow tube is oriented parallel to the length of thefilter. The distributor comprises at least one open end which is influid communication with an inlet in the housing. For example thedistributor may communicate directly with an inlet 101 as in FIG. 4, ormay communicate with an inlet region 118 which in turn is incommunication with one or more inlets 101 as in FIG. 3.

The distributor may extend the entire length of the filter and has oneor more openings along its length which distribute the fluid to selectedportions of the filter surface. The one or more openings in thedistributor may be substantially perpendicular to the length of thedistributor. The openings may, for example, be circular holes, forexample for ease of manufacturing, but they may also be polygons, slotsor any number of suitable shapes. The openings may include tubes orother features which extend outward from the distributor towards thefilter surface and direct fluid to the filter surface. A distributor 310with openings 314 is illustrated in FIG. 11.

In some embodiments, through a rotation of 360 degrees, the distributorcan sequentially direct fluid to the entire working surface of thefilter. In the embodiment shown in FIG. 11 there are multiple openings314 which all have the same size. By way of example the openings may becircular holes with a diameter of about 0.25 inches and a center tocenter spacing of about 0.50 inches along the length of the distributor.In other embodiments multiple openings in the same distributor havedifferent sizes. It is generally advantageous to size the openings inorder to balance the amount of flow and pressure being distributed toeach selected portion of the filter. Thus the openings may getprogressively larger as they get farther away from the inlet and/or theopening in the distributor that is in communication with the inlet. Thismay take the form of circular holes which get progressively larger indiameter as they get farther away from the inlet in the housing.

In some embodiments the openings point radially outward from the axis ofthe distributor. In other embodiments the openings are offset from theaxis of the distributor and point substantially along a line tangent tothe axis of the distributor. Openings which are offset from the axis ofthe distributor produce flow with a velocity component that istangential to the filter's surface. In some embodiments of the inventionthe tangential velocity helps to rotate the cleaning assembly.Additionally, this crossflow may delay fouling and increase performance.

When the cleaning assembly comprises both a distributor and one or morewipers the pattern of openings may match the shape of the wipers. Thisis illustrated, for example, in FIGS. 11 and 12, where the pattern ofopenings 314 generally matches the shape of the one or more wipers 316.Thus a spiral shaped wiper 316 will have a spiral pattern of openings314. In one embodiment the openings 314 are a spiral pattern of holes asshown in FIG. 11, and in another embodiment they are one or more spiralshaped slots as shown in FIG. 12. The size of the openings may varyalong the length of the distributor. For example, the slot width mayvary along the length of the distributor 310. The slot width mayincrease with distance from the inlet into the distributor.

When there is more than one wiper, there will generally be a pattern ofopenings associated with each wiper. The pattern of openings mayalternate with the wipers such that each two wipers have a pattern ofopenings between them.

Cleaning Assembly—Support and Drive

The cleaning assembly may be supported at one or both ends by one ormore bearings, examples of which are ball bearings and journal bearings.In the embodiments illustrated in FIG. 4 and FIG. 13, the cleaningassembly 300 is supported by a sleeve bearing 330 on the inlet tube 118which extends into the housing. One or more seals, such as o-ring seals322 may also be included to restrict fluid travel around the bearings. Adrive shaft 404, which penetrates the lid 401, may also be supported byone or more bearings and sealed by one or more seals. The drive shaftmay be coupled to the cleaning assembly 300 using, for example, a splinedrive, square drive or interlocking face gears. The lid assembly 400comprises a motor 402 which couples to the drive shaft 404 and drivesthe rotation of the cleaning assembly 300. The lid assembly with motor402 and shaft 404 can be removed from the housing, thus decoupling theshaft 404 from the cleaning assembly 300. In another embodiment thedistributor does not get decoupled from the lid assembly but insteadgets removed together with the lid assembly. In further embodiments, asillustrated in FIGS. 2 and 3 and further illustrated in FIG. 14, thecleaning assembly is entirely supported by a drive shaft which issupported by bearings and seals at one end of the housing. A motor 402,outside of the housing, couples to the drive shaft 404 and drives therotation of the cleaning assembly 400.

In even further embodiments the cleaning assembly is driven by othermechanisms, such as by hand or by turbine. A turbine may be located suchthat fluid flowing into the housing passes through the turbine and turnsthe cleaning assembly. For example, in the embodiments illustrated inFIGS. 2 and 3 the cleaning assembly may comprise a turbine (not shown)located in the inlet region 118 of the housing. Fluid passing from theinlet region 118 to the distribution region 210 would pass through theturbine driving rotation of the cleaning assembly. In the embodimentillustrated in FIG. 13 a turbine (not shown) may be located inside thedistributor 310 such that fluid passing from the inlet tube 118 to thedistributor 310 causes rotation of the cleaning assembly 300. In thisway no external power source is required to drive the cleaning assembly300. The power of the flowing fluid may alone provide the drivemechanism.

Cleaning Assembly—Inlet Region Divider

In some embodiments, one or more dividers are used to direct fluid inthe housing, such as to direct fluid from the inlet to the distributor.For example, when the cleaning assembly, as in FIG. 14, comprises adistributor 310 which is open at one end to an inlet region 118, it canbe advantageous to divide the inlet region 118 from the distributionregion 210. In this embodiment a divider 345 protrudes radially outwardfrom the distributor 310 forcing fluid to flow through the distributorto reach the filter. In one embodiment the structure engages the insidewall of the filter assembly or housing through a bearing, seal or both.In another embodiment the divider does not engage the filter assembly orhousing and instead allows a small amount of fluid to leak around thedivider. In other embodiments the divider is attached to the filter orhousing and protrudes inward towards the distributor.

Cleaning Assembly—Collection Region Divider

In some embodiments the rotation of the cleaning assembly drivesparticles towards one end of the housing where the particles collect ina collection region. The collection region and the cleaning assembly aregenerally configured to push particles towards the drain outlet. In someembodiments, a divider may separate the inlet region or unfilteredregion from the collection region.

When the cleaning assembly comprises a distributor 310, the distributormay not have openings 314 in this region, as in FIG. 3, to avoidturbulence, but may or may not have wipers 316. Wipers 316 in thecollection region 116 may be straight, spiral or take other usefulshapes and may or may not engage the housing wall. In the embodimentillustrated in FIG. 4 the same wipers which engage the filter continuethrough the collection region 116 to the end of the housing. In otherembodiments additional wipers are arranged on the cleaning assembly toengage the end of the housing.

It can be advantageous to physically divide the collection region fromthe distribution region to avoid particles returning to the filtersurface. In the embodiments illustrated in FIGS. 2 and 3 and thoseillustrated in FIGS. 11 and 12 this is accomplished by a divider 325which rotates with the distributor. In other embodiments the divider isnon-rotating and instead affixed to the filter wall or housing wall. Infurther embodiments a rotating divider 325 is used in conjunction with afixed divider.

The divider may have one or more openings, generally located adjacent tothe filter wall, which are configured to allow particles to easily enterthe collection region 116, but to resist particles returning to theunfiltered distribution region 210. Depending on their form, the one ormore openings may be fixed or rotating, or a combination of the two. Thedivider may consist of a flexible wiper like a brush or squeegee, or maytake the form of a rigid structure; or a combination of flexible andrigid structures. In the embodiment illustrated in FIG. 15 the divider325 is formed by a continuation of the cleaning wipers 316 and protrudesfrom the rotating distributor 310. The wiper wraps around thedistributor 310 forming an external arc. An opening 332 is formed byending the arc before the wiper wraps back around on itself or anotherwiper.

Cleaning Assembly—Operation

The cleaning assembly may be operated in one or more modes. In someembodiments the cleaning assembly is rotated at a single constant ratewhenever a fluid pumping system is turned on. In other embodiments thecleaning assembly is rotated at one of multiple fixed rates depending onthe level of filter fouling detected. Fouling of the filter materialgenerally causes reduced flow and increased transmembrane pressure. Thiscan be detected through pressure sensors, flow sensors and otherssensors known to someone skilled in the art. By way of example, pressuresensors may take the form of a pressure switch which turns on when a settransmembrane pressure level has been reached. They may also take theform of an electronic pressure transducer which produces an electricaloutput proportional to the differential pressure across the filtermaterial.

The rotational rate of the cleaning assembly may also be set to beproportional to the solids content of the influent. This can beaccomplished using one or more sensors also known to someone skilled inthe art, examples of which are turbidity sensors and suspended solidssensors. A still further mode would be to set the rotational rateproportional to the concentration of only those particles likely tocause fouling. This could be accomplished through the use of a particlecounter on the influent or a combination of suspended solids sensors atthe inlet and filtered outlet. Thus, the filter system may be configuredto adjust the rotational speed of the cleaning assembly in response to asignal from one or more of a turbidity sensor, a suspended solids sensorand a particle counter.

The cleaning assembly may contain one or more wipers such that a singlerotation of the cleaning assembly will wipe a section of filter materialone or more times. The wipers may pass over a section of filter materialfrom once per second up to 20 times per second, but each section offilter material could be wiped less or more often. By way of example, acleaning assembly having 4 wipers and rotating at 150 RPM would wipe thefilter 10 times per second.

Cleaning Assembly—Efficiency

With a surface filter such as those described herein, the retentiveforce on the pore-blocking particles is created by the transmembranepressure acting on the area of the particles that is blocking the pore.Fouling may result when the retentive force on the particles is greaterthan the motive force imparted by the wiper. Different wiper designswill be more or less effective at cleaning particles of different makeup. The effectiveness of the wiper can be characterized by a cleaningefficiency factor. The cleaning efficiency for a given wiper design isdependent, in part, on the pore width and transmembrane pressure. Thecleaning efficiency generally remains substantially 100% until acritical pressure is reached at which time it quickly drops to 0% aspressure continues to increase. At or above the critical pressure, thewipers are not able to affect pore-blocking particles of ever increasingdiameter. Operating beyond the critical transmembrane pressure creates adecaying flux curve, or in other words, the critical transmembranepressure is the pressure above which the total filtrate rate drops overtime. By way of example the critical pressure for a screen with 20micron wide slots and nylon brushes with 0.006 inch diameter nylonfilaments is approximately 3 psi and may be as little as 2 psi or even 1psi. In one embodiment of the invention the filter system is operatedcontinuously below the critical transmembrane pressure. In anotherembodiment the filter system operates above the critical pressure, butperiodically drops below the critical pressure for a short period oftime allowing the wiper to clean the filter. The critical pressure canbe determined by monitoring filtration rates at various pressures overtime and determining the pressure at which cleaning efficiency drops offto unacceptable levels.

Transmembrane Pressure Regulation

Operation of the filter system to control transmembrane pressure, forexample to operate below the critical transmembrane pressure, can beaccomplished in a number of ways. In some embodiments of the inventionthe filter system is supplied by a variable speed pump, which iscontrolled by drive electronics and a differential pressure transducer.The drive electronics change the speed of the pump impeller which variesthe flow and pressure output of the pump in order to produce arelatively constant transmembrane pressure.

In other embodiments the filter system is supplied by a single speedpump and additional components are used to regulate the transmembranepressure. An exemplary filter system along with additional fluid systemcomponents is represented schematically in FIG. 16. When the filtersystem is supplied by a single speed pump 512, the decreased flow offilter fouling causes an increase in the pressure supplied by the pumpand subsequently an increased pressure at the unfiltered region of thehousing.

Transmembrane pressure can be maintained by reducing the pressure in theunfiltered region of the housing or increasing pressure on the filteredregion of the housing. In one embodiment of the invention flow isrestricted at the inlet by a fluid system component 509 thus reducingthe pressure at the unfiltered region, as illustrated in FIG. 16. Thiscan be accomplished by a passive regulator, examples of which arepressure regulators and differential pressure regulators; or a flowcontrol valve, examples of which are ball valves and butterfly valves.In another embodiment flow is restricted at the filtered outlet 511 by afluid system component 503, thus increasing the pressure on the filteredregion of the housing. This can be accomplished using a flow controlvalve or a passive regulator, examples of which are back pressureregulators and differential back pressure regulators.

In some embodiments the transmembrane pressure is maintained with thecombination of a pressure regulator at the inlet and a back pressureregulator at the filtered outlet. In some embodiments a differentialpack pressure regulator is located at the filtered outlet and a pressureregulator is not located at the inlet. In still other embodiments, adifferential pressure regulator is located at the inlet and a backpressure regulator is located at the filtered outlet.

In some embodiments flow is increased at the drain outlet 506 using aflow control valve or a pressure release valve. The increased flowthrough the inlet lowers the pressure supplied by the pump and thuslowers the pressure on the unfiltered region of the housing. In evenfurther embodiments flow restrictors at the outlet are used inconjunction with a pressure source to actively raise the pressure in thefiltered region of the housing, thus reducing the pressure differentialacross the filter material

In some embodiments a passive fluid and pressure reservoir 501 islocated functionally between the filter material and any regulator 503at the filtered outlet. This provides a reservoir to equalize thepressure and flow across the filter material when fouling occurs. Thisreservoir can take the form of an accumulator tank 501 or simply an airbubble trapped in the housing where it can communicate with the filteredregion of the housing.

Drain Purge

Particles collected in the collection region may be purged from thehousing by one or more methods. In some embodiments, the pump supplyingthe system is turned off and the drain valve is opened. The particlesand fluid in the housing then simply drain out. This could be useful,for example, for swimming pools and other consumer applications wherecost is an issue and routine maintenance is expected. In otherembodiments the drain valve is fully opened while the pump continuesrunning. This flushes the collection region while also causing a suddendrop in pressure in the unfiltered region of the housing. The drop inpressure can help to unclog any pores which might be retainingparticles. When a pressure and fluid reservoir exists at the filteredoutlet a small amount of fluid may flow backwards through the pores ofthe filter further helping to dislodge stuck particles. This passiveback flush can be further aided by simultaneously closing a valve thatis positioned at the filtered outlet after the pressure reservoir, suchas valve 503 in FIG. 16.

In further embodiments the filter system is operated while the drainremains only slightly open. A small fraction of the fluid, generally inthe range of 1% to 10%, passes out through the drain taking with it therejected particles. A continuous drain of this nature is often called abypass flow or a brine stream.

In even further embodiments the system is operated as a crossflowfilter. In such a configuration a certain amount of flow passes outthrough the drain and creates a flow velocity tangential to the surfaceof the filter. This tangential flow acts as a cleaning mechanism whichcan work by itself or in conjunction with the wipers to reduce oreliminate fouling. In crossflow applications the bypass flow isoptimally run at about 50% but can range from about 10% to 90%. In someembodiments the bypass flow makes a single pass through the filtersystem. In other embodiments the bypass flow is pumped back into thesystem and makes multiple passes through the filter.

It is also possible to purge particles from the system withoutsubstantially impacting the pressure or flow of the system. Someembodiments use a rotary valve located at the drain outlet. In someembodiments a valve element comprises one or more cavities which can beopened sequentially first to the collection region and then to the drainby the rotation of the valve element. In some embodiments a valveelement comprises a positive displacement pump. In some embodiments aseal around the valve element maintains the pressure in the collectionregion. The rotary valve and/or positive displacement pump can be drivenby a motor or by hand. In one embodiment the element is coupled to thedistributor and driven simultaneously. If coupled to the distributor itmay be coupled through one or more gears to reduce the rotational speedof the valve with respect to the distributor. A typical gear ratio wouldbe 1:100 but could be as low as 1:10,000 or as high as 1:1.

In one embodiment a valve is operated in a continuous fashion wheneverthe filter is in operation. In other embodiments one or more sensors orswitches operates the valve. The valve can be operated by a timer; inresponse to filter fouling; or in response to solids accumulation in thecollection region. Filter fouling can be indicated by an increasedpressure differential or decreased flow which can be detected bypressure and flow sensors. Solids accumulation can be detected by avariety of sensors, examples of which are optical sensors and acousticsensors. In one embodiment the valve is a separate unit attached to thedrain outlet. In other embodiments the valve is integrated into the endor side wall of the housing.

Housing Design

In some embodiments, for example as illustrated in FIGS. 17 and 21, ahousing comprises an inlet housing 610 and an outlet housing 620. Thetwo separate inlet and outlet housing parts 610, 620 may be joined, forexample by a band clamp 630 and may be sealed, for example with O-Rings,as illustrated in FIG. 21, but may be joined and sealed in any number ofother ways. The housing may further comprise a lid 640 which is joinedto the inlet housing, such as by a band clamp 650 and O-Rings, but mayalso be joined and sealed in any number of suitable ways. As illustratedin FIGS. 22 and 23, the inlet housing may include one or more inlets 615which communicate with the inside of the filter, for example asdiscussed elsewhere herein. FIG. 22 also illustrates how the distributor300 is disposed inside the inlet housing and FIG. 23 illustrates thefilter assembly inserted in the inlet housing. As illustrated in FIGS.20 and 25, in some embodiments the outlet housing comprises a filteredregion 700 and filtered outlet 710, which communicates with the filteredregion of the inlet housing. In some embodiments the outlet housingadditionally comprises a drain region 730 and drain outlet 740, whichcommunicates with the unfiltered inside of the filter.

Cleaning Assembly

The rotating cleaning assembly 300 may comprise a spiral shaped wiperand hollow support structure. In some embodiments the wiper comprisesbrush filaments and in one embodiment the brush filaments 810 protrudeoutward from the support structure in bunches, as in FIG. 18. Each bunchmay be affixed into holes which are drilled in the support structure. Inone embodiment each bunch is joined to the support structure using astaple. The pattern of bunches may comprise a single row or multiplerows of bunches taking a spiral pattern or other suitable shape. In theembodiment of FIG. 18 the cleaning assembly comprises a distributor andwiper but no dividers. In this embodiment the inlet region divider 345is stationary and located on the filter assembly 200 as shown in FIG.19. In some embodiments the filter assembly 200 comprises a wedge wirescreen and metal end caps. The outlet region divider may be stationaryand located on the outlet housing or may not be present as shown inFIGS. 20 and 25. In the embodiment illustrated in FIG. 20 the cleaningassembly is driven by a motor 850 that is mounted to the lid and coupledby a drive shaft. The cleaning assembly is additionally supported by apin that is coupled to the outlet housing.

Baffles and Other Flow Regulators

Fluid generally passes from inside of the filter to the outside of thefilter, after which it is undesirable for the fluid to flow back to theinside of the filter. However, in some situations this backflow mayoccur in certain areas of the filter and particulates may accumulate onthe outside of the filter. For example, backflow may cause the outsideof the filter to plug up with particulate in some areas. Since thecleaning assembly does not generally make contact with the outside ofthe filter, this can cause premature fouling. Besides backflow there maybe other undesirable fluid dynamics that may sometimes occur between theoutside of the filter and the housing, another example of which isstagnation zones. Regions of fluid may become stagnant in places such asnear housing walls, near internal corners and in regions where fluidpaths separate. A stagnation zone can cause particulate to settle out ofthe fluid stream and collect in the housing. These solids can obstructflow and if they grow to a certain size may even plug the filter fromthe outside. A further example of undesirable fluid dynamics is unevenflow across the filter screen. It is generally desirable to maintainequal flow across the entire surface of the filter. In this way one partof the filter does not wear or plug any quicker than other parts of thefilter.

The undesirable fluid dynamics, described above, may be at leastpartially alleviated by the addition of one or more flow-directingfeatures that direct the flow of filtered fluid between the outside ofthe filter and inside of the housing. In some embodiments the flowdirecting features are used without a cleaning assembly inside thefilter. For example the flow directing features may be used incombination with disposable bag or cartridge filters, or withself-cleaning filters like backflushing filters. In other embodiments acleaning assembly is located inside the filter. In some embodiments thecleaning assembly is a rotating cleaning assembly. The rotating cleaningassembly may be as described herein, but may take other forms. In someembodiments the cleaning assembly comprises a rotating distributor andone or more wipers.

In some embodiments the flow directing features comprise one or morechannels located between the housing and the filter assembly. In someembodiments flow-directing features comprise baffles 900, for example aspictured in FIG. 24, which extend from the inside of the housing 910 tothe outside of the filter assembly 920, or vice versa, thereby creatingone or more channels 930 that direct fluid passing through the filtertoward the outlet region 700 as illustrated in FIG. 25. In someembodiments channels may be formed or created in the housing itself. Thehousing, or at least the channel forming portion of the housing, may beadjacent to or contacting the filter, such that fluid passing throughthe filter is directed by the channels toward the filtered outlet. Insome embodiments channels may be formed or created in the filterassembly itself. For example, the filter assembly may comprise materialthat supports the filter while forming channels at intervals down atleast a portion of the length, as illustrated in FIG. 5. In someembodiments the portion of the filter assembly that forms the channelscontacts or is closely adjacent to the housing.

In some embodiments one or more channels extend the entire length of thefilter, while in some embodiments they extend a portion of the length ofthe filter, for example half of the length of the filter or more. Insome embodiments one or more channels begins at the top of the filter.In some embodiments, as illustrated in FIG. 20, the channels begin belowthe top of the filter, for example 1 inch below the top of the filter.The region 745 above the channels allows each and every channel in thefiltered region of the housing to communicate with an air release outlet750. In some embodiments the unfiltered region may additionallycommunicate with an air release outlet 760.

In some embodiments one or more baffles 900 extend the entire length ofthe filter. In some embodiments the one or more baffles extend a portionof the length of the filter. For example, in some embodiments two ormore baffles begin at the top of the filter (closest to the inlet) andextend the entire length of the filter. In some embodiments two or morebaffles begin at the top of the filter and run at least half way downthe length of the filter.

In some embodiments, as illustrated in FIG. 24, the baffles are affixedto the housing and extend toward the filter. This configuration ofbaffles may also facilitate insertion of the filter assembly into thehousing, as the baffles align the filter in the center of the housing.This may be especially advantageous with very long filters when thehousing is mounted in a horizontal orientation. In some embodiments thebaffles may be affixed to the filter assembly and extend toward thehousing. Such a configuration may also serve to align the filter in thecenter of the housing.

In some embodiments baffles extend the entire distance between thefilter and the housing, such that fluid movement is restricted to achannel. In other embodiments one or more baffles may extend only partof the way between the filter and the housing, such that they direct thefluid but fluid movement past the baffles, such as between channels, ispossible.

When baffles are present it is generally advantageous to locate thefiltered outlet at one side of the housing beyond where the baffles arelocated, though in some embodiments the outlet is located in the baffledarea. Baffles may be attached to the filter and/or filter assembly andextend outward or may attach to the housing and extend inward, or may beattached on both sides to both the filter and the housing. In oneembodiment the baffles and housing together consist of a singleextrusion of material, and in other embodiments the baffles areindividually, or in groups, bonded, welded or otherwise affixed to thehousing wall. They may extend the entire distance between the filter andhousing or they may extend only part of the way. Any number of bafflesmay be used. In the embodiment illustrated in FIG. 24 there are 8baffles 900. Other embodiments may have 2, 3, 6, 10 or other numbers ofbaffles. The baffles may all be evenly spaced or have uneven spacing. Insome embodiments the baffles are parallel and run along the axis of thehousing. In other embodiments the baffles may not be parallel and mayhave other advantageous configurations.

Channels 930 are created by adjacent baffles. These channels generallykeep the flow of the fluid all moving in one direction. For example,fluid that has passed through the filter material may enter the channelsand be directed toward the outlet region and the filtered outlet. Thebaffles may reduce the occurrence of vortices and stagnation zones whichcan cause backflow and particulate settling.

The material, thickness and shape of the baffles may be selected toachieve the desired channel size and/or to provide specific flowdirection and/or behavior. In some embodiments each channel has aconsistent cross section along its length, for example along the lengthof the filter housing. This may be achieved, for example, by selectingbaffles that are essentially parallel and of uniform size along theirlength. More fluid is generally flowing in the channel as the flow getscloser to the outlet. In channels where the cross section remainsconsistent, the fluid velocity increases as more flow enters thechannel. In other embodiments the cross section of each channel maychange size and/or shape at one or more points along its length, such asalong the length of the housing. In one embodiment the channels have across section that gets larger as the flow gets closer to the outlet.For example, this may be achieved by baffles that decrease in thicknessat one or more points along their length, by changing the thickness ofthe housing wall at one or more points, and/or by changing the thicknessof the filter assembly material, such as toward the bottom of thehousing. In some channels the shape and spacing of the channels isselected such that the fluid velocity may remain generally consistentthrough the length of the channel.

The channels may include other flow modifying features that influencethe flow of fluid as it passes from the filter to the filtered outlet.In some embodiments these flow modifying features may help keep solidssuspended and/or prevent backflow. In some embodiments one or more ofthe surfaces of one or more channel may comprise one or more flowmodifying features. For example, the housing wall and/or the surface ofthe baffles may not be smooth. In some embodiments one or more surfacesthat form a channel may have bumps, ridges or divots. These featurestend to create turbulent flow which may prevent the settling of solids.

In the foregoing specification, various exemplary embodiments have beendescribed. It will, however, be evident that various modifications andchanges may be made thereto without departing from the broader spiritand scope of the invention which will be set forth in the claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. A fluid filtration device comprising: a hollowhousing comprising an inlet and a filtered outlet; a hollow filterassembly located inside the housing and comprising a filter materialhaving an interior surface and an exterior surface; and one or moreflow-directing channels located between the filter assembly and theinside of the housing.
 2. The filtration device of claim 1, wherein theone or more channels comprises one or more baffles.
 3. The filtrationdevice of claim 2, wherein the one or more baffles are oriented with theaxis of the filter.
 4. The filtration device of claim 3, wherein the oneor more baffles run the length of the filter.
 5. The filtration deviceof claim 3, wherein the one or more baffles are attached to the housing.6. The filtration device of claim 5, wherein the one or more bafflesalign the filter in the housing.
 7. The filtration device of claim 3,wherein the channels have a consistent cross section throughout theirlength.
 8. The filtration device of claim 3, wherein the channelscomprise a cross section that varies along their length.
 9. Thefiltration device of claim 8, wherein the channels get wider in thedirection of flow.
 10. The filtration device of claim 1, wherein thechannels comprise bumps, divets or ridges.
 11. The filtration device ofclaim 1, wherein the one or more flow-directing channels are arranged todirect fluid that passes through the filter material toward the filteredoutlet.
 12. A method of filtering a fluid comprising: providing afiltration device comprising: a housing; an annular filter locatedwithin the housing; and one or more channels defined between the filterand the housing and that are oriented with the axis of the filter andextend along the length of the filter, feeding the fluid to the insideof the filter; and passing the fluid through the filter, wherein the oneor more channels direct the fluid toward an outlet region after thefluid passes through the filter.
 13. The method of claim 12, wherein theone or more channels are defined by one or more baffles.
 14. The methodof claim 13, wherein the one or more baffles are attached to the housingand extend toward the filter.
 15. The method of claim 13, wherein thebaffles align the filter within the housing.
 16. The method of claim 12,wherein the one or more channels each have a consistent cross sectionthroughout their length.
 17. The method of claim 12, wherein the one ormore channels comprise a cross section that expands along at least aportion of the length of the channel.
 18. The method of claim 12,wherein the channels extend along the entire length of the filter. 19.The method of claim 12, wherein one or more bumps, ridges or divots arelocated within the channel.
 20. The method of claim 12, wherein the oneor more channels are configured such that the flow rate of fluid throughthe channels is relatively constant.